Wednesday, February 1, 2012

One Per Cent - Whale acrobatics inspire a faster helicopter

Paul Marks, senior technology correspondent
Image: Tiny rubber bumps, akin to whale fin nodules, attached to the rotor blade (Credit: DLR)

The way the humpback whale, Megaptera novaeangliae, manages to perform underwater acrobatics and turn on a dime - despite having pendulous, outsize pectoral fins - has inspired aviation engineers in Göttingen, Germany to make a faster, quieter helicopter rotor blade.
A helicopter has a rotor whose aerofoil-shaped blades provides lift, directional control and forward thrust. As the rotor spins, the advancing blade - which is moving in the same direction as the craft - is travelling faster than the retreating blade on the opposite side. These different speeds make for turbulence, vibration and instability - especially during fast flight and whilst turning, when the retreating blade is more likely to lose lift and "stall". As a result, helicopter engineers spend a lot of time trying to minimise this effect.
Noting the humpback's agility in water, Kai Richter and colleagues at the German Aerospace Centre (DLR) wondered if something analagous to the bumps on its pectoral fins - known to provide lift underwater and boost the creature's buoyancy - could help them improve chopper design. Scaling those bumps down relative to a rotor's width, they made 6-millimetre-diameter rubber grommets and fastened 186 of them  to the leading edges of the rotors on a test helicopter (see picture, above).
It did indeed significantly delay stalling and the difference has already been noticed by test pilots, Kai says, providing a smoother ride. They have been encouraged enough by their results to file patents on the idea, and they now plan further tests. If their whale mimicry pans out, it won't involve clunky rubber grommets: the bumps would be milled into blades during manufacturing.

The humpback whale: agile despite its size (Credit: DLR) 

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